Hydraulic borehole mining devices of the type with which the present invention is concerned exhibit a good potential for mining underground coal, oil shale, tar sands, heavy oil sands, and other minerals from the ground surface with a minimum disturbance of the surface itself. This general technique involves the drilling of a borehole from the ground surface to the underground mineral deposit and the use of at least one high-pressure water jet produced by a jet nozzle directed to cut or otherwise provide fragmentation of the mineral deposit. A slurry jet pump is used to entrain, in a slurry, the fractured mineral particles, and to transport these particles back to the ground surface.
Heretofore, others have used hydraulic borebole mining devices to mine mineral particles at depths up to 500 feet. Fly, U.S. Pat. No. 3,155,177, which is hereby incorporated by reference, disclosed borehole mining to a 500 foot depth. This is set forth in column 21 at lines 66-69 of U.S. Pat. No. 3,155,177. Mining to this depth was accomplished via water pressure of a proper stream size and sufficient pressure generated through a pump means. Fly also disclosed increasing the ascending velocities of the jet pump discharge fluids by controllably injecting additional water in the well or mined reservoir. Additionally, Fly disclosed that materials such as liquid butane and propane commonly known as liquified petroleum gas could be used as the hydraulic liquid to maintain a substantially higher pressure in the venturi and maintain such material in the liquid state under the temperature and velocity conditions there existing. This is disclosed in U.S. Pat. No. 3,155,177 at column 19, lines 42-58.
Recovery of minerals by hydraulic mining and jet pumping of aqueous mineral slurries is well known. For example, Redford, U.S. Pat. No. 3,951,457, discloses the hydraulic method in which hot water or steam is introduced into a subterranean deposit at high velocity to dislodge bitumen and particles of sand from the surrounding mineral bed. The resulting aqueous pulp is pumped to the surface by means of another high velocity jet of hot water or steam. Pfefferle, U.S. Pat. No. 3,439,953, discloses another apparatus for hydraulic mining. The U.S. Department of the Interior, Bureau of Mines, has sponsored development of a tool for single borehole slurry mining in which a stream of cutting jet water is pumped at very high pressure to a point adjacent the bottom of the borehole and is directed generally laterally at very high velocity into the surrounding mineral body to dislodge the mineral and form an aqueous pulp. The aqueous pulp is conveyed to the surface using a jet pump powered by a second stream of high pressure, high velocity water. Additional information on this system is available to the public from Flow Industries, Inc., 21414 68th Ave. South, Kent, Wash, 98031. A pneumatic sampling apparatus in which mineral is sampled and conveyed from below and annular bottom opening is disclosed by Murrel, U.S Pat. No. 3,807,514.
Hodges, U.S. Pat. No. 4,275,926 discloses metering the flow of slurry at the orifice of the venturi by use of a feed screw. The metered flow was augmented by controlling the rotational speed of the tool through the surface drive unit, which in combination with the adjustable opening yields a maximum efficiency ratio of solids into the flow stream. This maximum efficiency ratio was dependent upon the particular composition and consistency of the mined material but was typically within the range of 10 to 50 percent solid to liquid.
A problem associated with hydraulic borehole mining tools operating in deep wells is the high volume of water or liquid required for the process. These high volumes of water produced in the process must be separated from the mined slurry which adds to the cost and efficiency of the process. Also, in some mining areas abundant water or required liquids might be unavailable.
To use conventional borehole devices to remove the mined particles at depths of from about 1000-2000 feet would require large capacity pumps and nozzles. This usage would result in costly equipment requirements. The present invention circumvents these requirements by using compressed natural gas or inert gases to serve as the lifting force to raise slurried mineral particles to the surface without the assistance of a slurry pump.